Manufacture of low-tension sparking



n Gm .mm MN AE7 P 5 I SWW NW mOn P Ch .WL ...www FRn.. 0mm?. N MI T MF U N A M June 14,121960' United States Patent O MANUFACTURE F LOW-TENSION SPARKING PLUGS FR INTERNAL COMBUSTION ENGINES Lucien Pras, Billancourt, France, assignor to Regie Nationale des Usines Renault, Billancourt, France Filed Jan. 2, 1957, Ser. No. 632,048

Claims priority, application France Jan. 11, 1956 2 Claims. (Cl. 49-81) Many forms of low-tension sparking plug electrodes have already been proposed, wherein the spark occurs across two electrodes by the discharge of a condenser to ignite the air-fuel mixture of internal combustion engines. The problem of incorporating an insulator between the electrodes, due to the very narrow gap available (ie. from 0.004" to 0.012") is extremely diicult to solve and reduces the range of materials that can be used for this purpose inasmuch as this insulator must have the property of enabling the spark to glance olf on its surface while offering a convenient mechanical and thermal resistance thereto.

Now this invention relates more particularly to an improved method of manufacturing the insulated electrode unit of low-tension sparking plugs, wherein the insulator consists of glass, notably borosilicated glass.

According to the present invention, ,the glass is ground to a tine powder and forms a suspension in water or in another organic liquid, this suspension having a pasty consistence. Then, this paste is either applied with a brush or gtm-sprayed on to the surface of .the metal parte, the latter -being accurately scoured and slightly oxidized beforehand by rapidly heating them to dark red heat. After the suspension liquid has evaporated ot, the coated parts are heated in atmospheric air or in a nitrogen atmosphere at such temperature that the glass particles melt and form a continuous vitriiied or Iglazed film adhering strongly on the metal surfaces. By applying several coats of glass alternating with heating steps it is possible to form relatively thick glass layers on the metal. These electrodes are assembled upon completion of the vitriication, when the hot mass of glass has a pasty consistence, whereby it may flow back, both inand outside, to fill the space between the electrodes.

The application of this method to a conventional electrode arrangement is illustrated by way of example in the accompanying drawing, wherein Fig. l shows a pair of concentrical electrodes 1, 2 coated separately as set forth hereinabove, then dried, glazed and disposed in the proper relative positions when lthe mass of hot, pasty glass ows back in the space 3 between the electrodes so as to till it. When the assembly has cooled down to room temperature the lower face is ground slightly to remove any excess material which may have flowed outwards and to form a spark `gap level with the concentric electrodes.

This method of applying a glass insulation on low-tension sparking plug electrodes may be associated with the combined use of another insulating material. In this case, the glazed or vitried electrodes are ground and lapped.

Figure 2 of the drawing illustrates in axial section au electrode assembly constituting a typical example of the simultaneous use of the two insulators.

This assembly comprises two electrodes, i.e. a hollow 2,940,221 Patented June 14, 1960 the lower face of the electrode is lightly lground untilr a surface is obtained wherein the metal electrode 4 appears in the 4form of a annulus about 0.016" thick around a wider annulus of insulating material. Then, a mica washer 6 is so applied on this surface that the latter is engaged by the upper face of the washer up to the bevelled portion. 'Then the other electrode 7 is placed against the washer 6 and held in position by a central rod 8 of .conducting material and a nut 9.

I claim:

1. 'The method of manufacturing a surface discharge spark plug for operation with a discharge condenser in low tension ignition installations which consists of providing a tirst metallic electrode having an axial bore and a sparking surface and a second metallic electrode having a sparking surface to be assembled coaxially with the rst electrode with their sparking surfaces closely spaced and substantially ilush and providing insulating material comprising borosilicated glass to be used as an insulating core between the electrodes, and to form a surface substantially coplanar with .the sparking surfaces prior to assembly of the electrodes, reducing the glass to a powdered state, adding liquid to the powdered glass to form a composition of a substantially viscous consistency, applying the composition to the electrode surfaces .to be assembled, prior to assembly thereof, treating .the electrodes in an unassembled condition with heat suicient to melt the glass particles and fuse them thereby to vitrify the composition, repeating .the application of the composition and the vitrication thereof to form successive thin layers of insulating material on the electrodes, heating the electrodes in an unassembled condition with all of ,the layers of insulating material thereon suiciently to cause the insulating material to assume Va plastic state in preparation for yassembling .the electrodes, assembling the electrodes by disposing 4them coaxially and moving them in a direction opposite Vto each other after a final Iapplication and vitrification of .the composition while the composition is in a heated and plastic state, and cooling the assembled electrodes.

2. The method according to claim 1, in which prior .to the application of .the composition to the electrode surfaces .the electrodes are oxidized by rapidly heating them to a dark red.

References Cited in the tile of this patent UNITED STATES PATENTS 1,562,533 Weintraub Nov. 24, 1925 1,775,218 Thurneyssen Sept. 9, 1930 2,125,315 Ronci Aug. 2, 1938 2,136,052 Hurley Nov. 8, 1938 2,248,644 Reger et al. Iuly 8, 1941 2,293,381 Carington Aug. 18, 1942 2,399,770 Taylor May 7, 1946 2,422,628 McCarthy June 17, 1947 2,429,955 Goldsmith Oct. 28, 1947 2,436,644 Halstead Feb. 24, 1948 2,549,504 Messana Apr. 17, 1951 2,560,593 Pask et al. July 17, 1951 2,657,248 Smits Oct. 27, 1953 2,709,147 Ziegler May 24, 1955 

